The present disclosure relates to high temperature electric discharge lamps. It finds particular application with regard to lamps that experience emitted light loss in the infrared region, which generally accounts for an energy loss of up to about 70%. However, it is to be appreciated that the present disclosure will have wide application throughout the lighting and photovoltaic industry.
Resistively or non-resistively heated light sources, including incandescent and discharge lamps, generally lose a majority of the emitted wavelengths in the infrared region of the spectrum, which translates into what may be as high as a 70% energy loss for the lamp to non-visible light output. Of this, roughly 2% may be lost to ultraviolet emissions, while the rest is lost to convection emission. Because this energy remains in the lamp envelope, tungsten, which has a very high melting point, greater than about 3200° C., has historically been employed for use as a filament and electrode material.
With the invention of thin film technology, lamp efficiency increased due to the application of ultraviolet and infrared reflective coatings being applied to the filament and/or electrode to direct at least a portion of the discharge back to the filament. While this technology was able to reduce energy losses with about a 50% efficiency rate, it nonetheless does not address the issue of suppression or conversion of unwanted light emissions.
A means of suppressing unwanted wavelength emissions was disclosed in U.S. Pat. No. 5,079,473. This disclosure is directed to the use of a radiating device having microcavities with a cavity diameter suitable for suppressing 700 nm and above wavelengths. This device, however, suffers from structural instability at temperatures as low as about 1200° C., even though the melting point of tungsten is far above that. Later innovators were able to gain stability at temperatures up to about 2000° C. by employing a nanocavity surface treated with tungsten carbide, or by use of a wire structure made from a refractory material, exhibiting wavelengths of 780 nm or less, and therefore having wavelength suppressing properties above this range.
Another attempt to address the issue involved the transfer of a nanoscale pattern to the filament using a mask of a material such as titanium, chromium, vanadium and tungsten, and their oxides in the presence of a polymer resist to achieve the pattern transfer. Also, alumina film and anodized alumina film have been used to generate pore structures on substrates, and plasma etching techniques have been used to generate surface roughness, or mounds, that increase the emissivity of tungsten.
The foregoing, while advancing the technology to some degree, fail to fully address the issue of wavelength suppression and shift to generate emissions of the shifted wavelengths in the visible range, thus increasing lamp efficiency. The invention disclosed herein is intended to provide a process for the creation of a photonic lattice on the surface of an emissive substrate comprising first depositing a thin film metal layer on at least one surface of the substrate, the thin film metal comprising a metal having a melting point lower than the melting point of the substrate, then annealing the thin film metal layer and the substrate to create nano-particles on the substrate surface, and anodizing the annealed thin film metal and substrate to create pores in the nano-particles and the substrate such that upon exposure to high temperature the emissivity of the substrate is refocused to generate emissions in the visible and lower infrared region and to substantially eliminate higher infrared emission, and the substrate thus created.